London (CNN) -- Celebrity chef Nigella Lawson said she was "ashamed" of her drug use but preferred to be honest, as she took the stand for a second day Thursday as a witness in the fraud trial of two former personal assistants.

Quizzed again on the subject Thursday, she said, "I have been frank, and the fact is I would rather be honest, if ashamed, and explain the drug use rather than be bullied with lies about something that happened in a humiliating and very public way."

In light of her tribulations, she described 2013 as "the longest year of my life."

Nigella Lawson Testifies

The former aides, Italian sisters Francesca and Elisabetta Grillo, deny embezzling hundreds of thousands of pounds on Saatchi's company credit cards while employed by Lawson and Saatchi.

Lawson was also asked again Thursday about her initial reluctance to come to court.

The allegations of drug use emerged in June, around the time Lawson and Saatchi were photographed having an argument in a restaurant, Scott's.

In the photos, which were splashed across the front pages of national newspapers, Saatchi is seen with his hand around Lawson's throat and appears to pinch and look up her nose. Saatchi accepted a police caution for assault, and the couple announced they would divorce soon afterward.

Lawson told the court the only thing she objected to was the story "that I was taking drugs at Scott's," a reference to an alleged claim by Saatchi that he was wiping cocaine from her nose at the restaurant.

Asked why she hadn't sued Saatchi for libel over the claim, Lawson said that she didn't have the money and did not want to go to court because her ex-husband enjoyed litigation.

"I do not appreciate being bullied. I am not going to continue to be bullied," she said.

Lawson said she felt it was her duty to come to court in this case. "I felt it would be an unpleasant experience, but that's not an excuse not to do one's civic duty."

Referring to Saatchi's request for her to attend the trial, made in a letter sent by his lawyers,Lawson said Wednesday: "He had said to me if I didn't get back to him and clear his name, he would destroy me."

Francesca Grillo's lawyer questioned Lawson on Thursday about exactly what her client was responsible for paying for.

Lawson rejected the notion that Francesca had been given free rein to use the credit cards.

"There were not written-down rules. ... But it was known that they were not for personal use unless directed," Lawson said. "I don't think any normal person would think that someone else's credit card was for their personal use."

Lawson said she disputed "completely" the claim that Francesca had given money to her two children and stepdaughter to pay for lunches, dinners, public transit and excursions amounting to 29,000 pounds in one year. She also hit out at Francesca's lawyer for raising personal details about her children.

Francesca Grillo's lawyer listed a number of purchases of luxury goods made on the company credit card, including 7,000 pounds at Chanel in St. Tropez, which her client said had been approved by Lawson as a treat.

Lawson responded, "7000 pounds of designer wardrobe! No, I would not have said that."

Asked if she had noticed that her personal assistant wore designer clothing, Lawson said Francesca had always claimed they were knock-offs or bought from a sample sale.

'I did not have a drug problem'

Lawson denied defense allegations Thursday that she kept cocaine in a jewelry box, or that rolled-up notes used for snorting drugs were left around her house.

"People who are regular cocaine users do not look like this," the TV star said, gesturing to her body and face.

Lawson said she was a sole parent who looked after herself. "If you think I am going to sabotage my health and risk leaving my children as orphans, you are very wrong," she said.

Lawson told the court Wednesday that she had used cocaine about six times with her late husband, John Diamond, when he learned that his cancer was terminal, in order to give him "some escape from his treatment."

She also used cocaine once in July 2010 when she felt subject to "terrorism" by her then-husband, Saatchi, she said. At that point she felt trapped, isolated and unhappy, she said, and a friend offered her the drug.

Lawson also admitted using cannabis but said she has given it up. She said she took the prescription drug Xanax only as instructed by her doctor.

Lawson insisted, "I've never been a drug addict, I've never been an habitual user. ... I did not have a drug problem, I had a life problem."

Saatchi had claimed in an e-mail that Lawson had used drugs regularly, but in testimony Friday, he backed off that claim.

In the e-mail, which was shared with the court by the defense in a pretrial hearing, Saatchi wrote that the assistants would probably "get off" because Lawson was using cocaine and marijuana on a daily basis and "allowed the sisters to spend whatever they liked."

Lawson, whose culinary skills and flirtatious manner have long entranced UK audiences, has also appeared as a judge on ABC show "The Taste" in the United States. A second season of the show is due to air in January.